运行包含管道的命令行并将结果显示到STDOUT

How would one call a shell command from Python which contains a pipe and capture the output?

如何从Python调用包含管道并捕获输出的shell命令?

Suppose the command was something like:

假设命令是这样的:

cat file.log | tail -1

The Perl equivalent of what I am trying to do would be something like:

Perl相当于我想要做的事情就像:

my $string = `cat file.log | tail -1`;

5 个解决方案

#1

Use a subprocess.PIPE, as explained in the subprocess docs section "Replacing shell pipeline":

使用subprocess.PIPE,如子流程文档部分“替换shell管道”中所述:

import subprocess
p1 = subprocess.Popen(["cat", "file.log"], stdout=subprocess.PIPE)
p2 = subprocess.Popen(["tail", "-1"], stdin=p1.stdout, stdout=subprocess.PIPE)
p1.stdout.close()  # Allow p1 to receive a SIGPIPE if p2 exits.
output,err = p2.communicate()

Or, using the sh module, piping becomes composition of functions:

或者,使用sh模块,管道成为功能组合:

import sh
output = sh.tail(sh.cat('file.log'), '-1')

#2

import subprocess
task = subprocess.Popen("cat file.log | tail -1", shell=True, stdout=subprocess.PIPE)
data = task.stdout.read()
assert task.wait() == 0

Note that this does not capture stderr. And if you want to capture stderr as well, you'll need to use task.communicate(); calling task.stdout.read() and then task.stderr.read() can deadlock if the buffer for stderr fills. If you want them combined, you should be able to use 2>&1 as part of the shell command.

请注意,这不会捕获stderr。如果你想捕获stderr,你需要使用task.communicate();如果stderr的缓冲区填充,则调用task.stdout.read()然后task.stderr.read()会死锁。如果你想要它们的组合,你应该能够使用2>&1作为shell命令的一部分。

But given your exact case,

但鉴于你的具体情况,

task = subprocess.Popen(['tail', '-1', 'file.log'], stdout=subprocess.PIPE)
data = task.stdout.read()
assert task.wait() == 0

avoids the need for the pipe at all.

根本不需要管道。

#3

This:

import subprocess
p = subprocess.Popen("cat file.log | tail -1", shell=False, stdout=subprocess.PIPE, stderr=subprocess.PIPE, stdin=subprocess.PIPE)
#Try shell=True if the above doesn't work with shell=False
p_stdout = p.stdout.read()
p_stderr = p.stderr.read()
print p_stdout

Or this should work:

或者这应该工作:

import os
result = os.system("cat file.log | tail -1")

#4

Another way similar to Popen would be:

另一种类似于Popen的方式是:

command=r"""cat file.log | tail -1 """
output=subprocess.check_output(command, shell=True)

#5

This is a fork from @chown with some improvements:

这是@chown的一个分支,有一些改进:

an alias for import subprocess, makes easier when setting parameters

导入子进程的别名,在设置参数时更容易

if you just want the output, you don't need to set stderr or stdin when calling Popen

如果你只想要输出,那么在调用Popen时你不需要设置stderr或stdin

for better formatting, it's recommended to decode the output

为了更好的格式化,建议解码输出

shell=True is necessary, in order to call an interpreter for the command line

shell = True是必要的,以便为命令行调用解释器

#!/usr/bin/python3

import subprocess as sp

p = sp.Popen("cat app.log | grep guido", shell=True, stdout=sp.PIPE)

output = p.stdout.read()
print(output.decode('utf-8'))

$ cat app.log 
2017-10-14 22:34:12, User Removed [albert.wesker]
2017-10-26 18:14:02, User Removed [alexei.ivanovich] 
2017-10-28 12:14:56, User Created [ivan.leon]
2017-11-14 09:22:07, User Created [guido.rossum]

$ python3 subproc.py 
2017-11-14 09:22:07, User Created [guido.rossum]

#1